The present invention relates to a metallocene catalyst based on a transition metal from group 4 or 5 of the periodic table which is supported by hybrid catalyst supporting means with aliphatic organic groups.
One also describes the process for supporting metallocene on said hybrid catalytic supporting means with aliphatic organic groups.
The main advantage of the supported metallocene catalyst of the present invention is that an ethylene polymer with broad or bimodal molar mass distribution is produced by using only one type of metallocene complex on the supporting means. As a result, the resin produced can be processed in an improved manner, and one obtains a potential reduction of processing costs.
There are many researches involving the development of metallocene catalysts. These catalysts, due to the fact that they have a single active center, enable the production of polyolefins with properties that are differentiated in terms of molecular mass, molar mass distribution, stereoregularity and incorporation and co-monomer distribution.
Particularly, polymers that have a narrow distribution of molar mass exhibit better physical properties, such as resistance to impact and to “environmental stress cracking”, as well as film transparency. However, these polymers exhibit processing difficulty due to their restriction in the distribution of molar mass.
In general, a broad distribution of molar mass provides greater fluidity of the polymer in the molten state, facilitating the processing thereof.
Thus, a few strategies for broadening the distribution of molar mass of polyolefins produced by using metallocene catalysts have been developed in the prior art. Among them we can cite: (i) blends of polymers produced by two different catalysts such as described in U.S. Pat. No. 6,649,698 and U.S. Pat. No. 6,787,608; (ii) use of multi-reactor technology as described in WO07336A1; U.S. Pat. No. 6,566,450; U.S. Pat. No. 7,488,790, and WO/2005/005493; (iii) combination of two metallocenes that are not supported on the polymerization of olefins, as mentioned in US. Pat. No. 0,234,547A1 and US2011257348A1; and (iv) polymerization of olefins by using a catalyst prepared by immobilizing two different metallocenes or one metallocene and one non-metallocene in the same support, as for instance in U.S. Pat. No. 719,302B2; U.S. Pat. No. 7,312,283B2; U.S. Pat. No. 6,943,134B2; U.S. Pat. No. 0,183,631A1; U.S. Pat. No. 5,525,678A; U.S. Pat. No. 7,199,072B2; U.S. Pat. No. 199,072b2; U.S. Pat. No. 6,686,306B2, and U.S. Pat. No. 6,001,766A.
The use of catalytic systems for polymerizing olefins comprising supported metallocene catalysts comprising inorganic supports is extensively described in the literature (Hlatky, Chem. Rev. 100 (2000) 1347-1376; Severn et alli, Chem Rev. 105 (2005) 4073-4147).
As can be seen from the prior art, silica has been the inorganic support at that is most widely employed in the development of supported metallocene catalysts. The surface and reactivity of the functional silica groups (isolated silanols, vicinal and geminal silanols, and siloxane) are well known. Obtaining them involves well-known pathways, among which is precipitation (precipitated silicas), and resulting from hydrolysis and reactions and condensation (xerogel silicas, aerogels, hydrogels). See, example, US 1970/3505785; US1971/3855172; DE1972/2224061; US1974/3668088; DE1975/2505191; US1975/3922393; DE1977/2719244; DE1976/2628975; US1979/4179431; EP1980/0018866; DE1986/3518738; DE1989/0341383; EP1989/0335195A2; US 1992/5118727 and US 1998/5723181.
Various pathways for preparing supported metallocene catalysts have been described in the literature and may be classified into:
(i) direct immobilization on silica as described in Santos et alli, Macromol. Chem. Phys. 198 (1997) 3529; Dos Santos et alli, J. Mol. Catal A; 139 (1999) 199; Dos Santos et alli, Macromol. Chem. Phys. 200 (1999) 751);
(ii) immobilization on silica functionalized with methylaluminoxane (herein referred to as MAO), or with other types of catalysts, as described in US1989/4808561; US1989/4871705; US1990/4912075; US1990/4914253; US1990/4925821; US1990/4935397; US1990/4925217; US1990/4921825; US1991/5026797; US1991/5006500; US1992/5086025; US1993/5328892; WO1994/26793; US1995/5462999; WO1996/04318; US 1995/5468702; EU1997/849286; WO1997/42228; US1997/5629253; US1997/5661098; EU1998/922717; EU1998/856525; US1998/5712353; US1998/5739368; US1998/5763543; US1998/5719241; EU1999/989139; US1999/5968864; EU2000/1038855; US2000/6034024; WO2001/12684; WO2001/40323; US2001/6214953; EU2001/1167393; US2001/0051587; US2001/0053833; EU2002/1231225; US2002/40549; US2002/0107137; US2003/236365 and WO2004/055070;
(iii) synthesis of metallocene situ on the support, as described in JP1990/0485306; US1996/5504408; US998/5739226; US2002/6399531; and US2002/326005;
(iv) Immobilization on hybrid silica, as described in: Dos Santos et alli, Appl. Catal. A: Chemical 220 (2001) 287-392; Dos Santos et alli, Polymer 42 (2001) 4517-4525; Dos Santos et alli, J. Mol. Catal. A: Chemical 158 (2002) 541-557; and
(v) Immobilization on silicas modified with spacers, as describes, for example, in US1995/5397757; US1995/257788 and US1997/5639835.
The pathway (i) consists of the reaction between the silica silanol groups and the group that gives off the metallocene (chloride or hydride) in the presence of an organic solvent. The pathway (ii) essentially comprises pre-contact of the support with MAO or other alkylaluminums, followed by immobilization of the metallocene. In the pathway (iii), the silanol groups of the silica surface are reacted with compounds of the type MCl4 (M=Ti, Zr) and then with indenyl or cyclopentadienyl ions, or the silanol groups of the silica surface are reacted organosilanes provided with ligands of the cyclopentadiene or indene type, which by deprotonation generate aromatic ions that may be metallized with reactants of the type MCl4 (M=Ti, Zr). Hybrid-silica immobilizing pathways (pathway iv) consist in obtaining a silica containing organic groups on the surface, obtained by the sol-gel method, followed by metallization. This pathway differs from the preceding one in that in pathway (iii) the silica employed is commercial, previously synthesized, whereas in the latter pathway the silica is synthesized already with the organic ligands (hybrid silicas). The pathway (iv) differs from the present invention in that the hybrid silica does not contain aliphatic organic groups and, therefore, does not generate a catalyst capable of producing polyethylenes that are bimodal or have broad distribution of molar mass. Finally, in the last pathway, the catalytic sites are generated or pushed off the surface (vertical spacers) or from each other (horizontal spacers). In both cases, the objective is to increase the catalytic activity of these supported metallocene catalysts.
In the open literature, examples of these five pathways are commented in the bibliographic revisions of Hlatky (Chem. Rev. 100 (2000) 1347-1376) and of Severn et al (Chem Rev. 105 (2005) 4073-4147). Examples of these methodologies can also be found in documents WO 2006/131704; WO 2006/131703; JP 2006/233208; US 2006/135351; US 2006/089470; JP 2006/233208; US 2001/6239060 and EP 2000/1038885.
Most patent documents that use chemically modified silica employs some type of commercial silica and modify it by grafting reactions or impregnation.
WO 2006/131704 describes the preparation of a supported catalyst, on which, after pre-contacting the co-catalyst with the catalyst (transition metal compounds, particularly metallocenes), in mole ration lower than 10:1, the mixture is contacted with a porous support, followed by removal of the solvent (impregnation method). The preparation method is simple, without implying loss of activity. The same thing happens in US 2006/089470, in which a homogeneous metallocene catalyst and a combination of alkylaluminoxane and alkylaluminum are supported on silica, with average size of 540 μm. Metallocene catalyst and co-catalyst (aluminoxane or alkylaluminum) are also pre-contacted before being immobilized on spheroidal silica (5-40 μm) according to patent EP 200/1038885. In this case, 50% of the catalytic component is immobilized inside the support pores, which guarantees the production of a product having few gel imperfections.
In WO 2006/131703, the porous support is pre-treated with a dehydrating agent and with a hydroxylated compound. The resulting support is then reacted with the catalyst (transition metal compound, such as metallocene, for example) and co-catalyst. The resulting supported catalyst is provided with enhanced catalytic activity. In document JP 2006/233208, the support is also pre-treated, but in this case with aluminoxane compounds, such as MAO, followed by reaction with metallocene. In this case, a part of the support is reacted with an ansa-metallocene and a part with an ansa-fluorenylmetallocen. In both cases, the metallocenes are individually treated with tri-isobutylaluminum (herein referred to as TIBA) and with 1-hexane. The final catalytic system is constituted by the combination of the two supported metallocenes and is active for co-polymerization of ethylene and 1-hexene. In US 2001/6239060, silica, after acidic treatment (HCl) and thermal treatment (110 and 800° C.), is functionalized previously with alkylaluminum and then contacted with metallocene-aluminoxane mixture. In WO 2002/038637, the process of preparing the supported metallocene catalyst is carried out by successive reaction of silica with ordinary alkylaluminum, and with borate derivatives, followed by addition of an ansa-metallocene. The final catalyst, active in the co-polymerization of ethylene and/or propylene with alpha-olefins, guarantees high contents of incorporated co-monomer.
Organoaluminums of the type Et2AlH and Et2Al(OEt) were proposed as silica modifying agents in document WO 2003/053578. The resulting silica served as a support for immobilizing metallocene. The resulting system exhibited an increase in catalytic activity, attributed to the additional presence of co-catalysts on the silica surface.
JP 2003/170058 describes the preparation of a support in which commercial silica pre-modified with ordinary alkylaluminum and with compounds having electroactive groups, such as 3,4,5-trifluorofenol. The modified silica is employed in the co-polymerization of olefins as a component of the catalytic system constituted by a metallocene and common alkylaluminum. This is no preparation of the final supported catalyst, but rather in situ immobilization, in which the ultimate heterogenization process takes place in situ, inside the polymerization reactor.
JP 2006/274161 teaches the preparation of active supported catalysts for co-polymerization of olefins, capable of polymerizing ethylene and 1-butene in the presence of common alkylaluminums and producing co-polymers with short branching and molar mass distribution (herein referred to as DPM) of 6.8. Such catalysts use silica functionalized with organometallic compounds with metal of the groups 1 and 2, as for example Et2Zn, which is then treated in a number of steps with electron-donating organic solvents, water, before the immobilization of an ansa-metallocene.
US 2006/135351 describes the preparation of the supported catalyst, wherein the metallocene has a functional group that facilitates and leads to a strong bond with the silica surface, used as support, minimizing bleaching processes. According to the technical description of this document, the polymerization takes place without “fouling” in the reactor, in both slurry process and in gaseous phase, and the morphology and density of the polymer produced are much better defined.
Lewis bases such as pentafluorofenol were also used in the modification of silica. The immobilization of metallocenes and organometallic compounds such as chromocene, on the same support (silica) modified with Lewis bases and alkylaluminum generate active catalysts in the co-polymerization of ethylene and 1-hexene, with DPM of 10.9.
WO 2004/018523 describes a process of preparing supported metallocene catalyst, in which the support (silica) is synthesized by a non-hydrolytic sol-gel process by condensing a silane containing anionic ligands, of a halogenated silane (r siloxane) and an alkoxysilane. The hybrid silica generated is then subjected to a metallization reaction, and the resulting catalyst is active, in the presence of a co-catalyst, in processes of polymerization olefins, in gaseous phase.
As can be seen from the prior art, it is not described or expected that the immobilization of a single metallocene complex on a silica-base support results in a polyethylene with broad or bimodal mass distribution. Moreover, the use of hybrid silica provided with aliphatic organic groups, prepared by the sol-gel process, as a support for metallocene was not reported in the literature.
Thus, the present invention relates to metallocene catalysts based on transition metal of the groups 4 and 5 of the periodic table, supported on a hybrid support for the production of homopolymers or copolymers of ethylene with alpha-olefins with broad or bipolar molar mass distribution.
One also describes a process of preparing metallocene catalysts supported on a hybrid catalytic support and a process for the production of homopolymers or copolymers of ethylene with alpha-olefins with broad or bimodal molar mass distribution.
The supported metallocene catalyst of the present invention exhibits, as its main advantage, the fact that it produces an ethylene polymer with broad or bimodal molar mass distribution using only one type of metallocene complex on the support. As a result, one obtains better processability of the resin obtained and, therefore, a potential reduction of the processing cost.